Initial implementation of custom postfix snippets

crates/ide_completion/src/config.rs

@@ -5,6 +5,8 @@
 //! completions if we are allowed to.
 
 use ide_db::helpers::{insert_use::InsertUseConfig, SnippetCap};
+use itertools::Itertools;
+use syntax::ast;
 
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct CompletionConfig {
@@ -15,4 +17,46 @@ pub struct CompletionConfig {
     pub add_call_argument_snippets: bool,
     pub snippet_cap: Option<SnippetCap>,
     pub insert_use: InsertUseConfig,
+    pub postfix_snippets: Vec<PostfixSnippet>,
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct PostfixSnippet {
+    pub label: String,
+    snippet: String,
+    pub description: Option<String>,
+    pub requires: Box<[String]>,
+}
+
+impl PostfixSnippet {
+    pub fn new(
+        label: String,
+        snippet: &[String],
+        description: &[String],
+        requires: &[String],
+    ) -> Option<Self> {
+        // validate that these are indeed simple paths
+        if requires.iter().any(|path| match ast::Path::parse(path) {
+            Ok(path) => path.segments().any(|seg| {
+                !matches!(seg.kind(), Some(ast::PathSegmentKind::Name(_)))
+                    || seg.generic_arg_list().is_some()
+            }),
+            Err(_) => true,
+        }) {
+            return None;
+        }
+        let snippet = snippet.iter().join("\n");
+        let description = description.iter().join("\n");
+        let description = if description.is_empty() { None } else { Some(description) };
+        Some(PostfixSnippet {
+            label,
+            snippet,
+            description,
+            requires: requires.iter().cloned().collect(), // Box::into doesn't work as that has a Copy bound 😒
+        })
+    }
+
+    pub fn snippet(&self, receiver: &str) -> String {
+        self.snippet.replace("$receiver", receiver)
+    }
 }